1. Field of the Invention
This invention relates generally to swivel devices used for rotating one object relative to another--such as a seat portion of a chair and a set of chair legs--and more particularly to a seat swivel that includes both a spring biasing member for maintaining a continuous and substantially constant force on the mounting plates of the swivel and a pair of bearing races having partial, flattened surfaces.
2. Prior Art
Conventional seat swivel devices usually include a top and bottom mounting plate, each having an annular channel which defines a race for holding a set of ball bearings. Generally, these swivel devices include fastening assemblies, such as a nut and bolt, which are fastened through pivot bores in each of the plates to maintain the plates in contact with the ball bearings. The plates can then rotate freely relative to one another via the ball bearings.
Typically, when a conventional swivel device is assembled, the nut must be fixed to the bolt to prevent the nut from loosening from the bolt during usage. This is usually done in a staking operation in which the nut is initially tightened to a location on the bolt which will maintain the plates in proper contact with the ball bearings. Thereafter, the end of the bolt is struck with a die forming a widened portion on the bolt that prevents the nut from loosening from the bolt. After this staking operation is performed, the nut is generally incapable of moving from its original, fixed position.
One major drawback in prior art devices that use this staking operation or any other operation to fix the nut to the bolt occurs when the swivel device becomes worn from usage. Even under normal conditions, the ball bearings, and particularly the bearing races, are subject to extreme frictional forces that results in some loss of metal from the inner surfaces of the races and from the ball bearings. The resulting wear to these surfaces causes the top and bottom plates to move closer to each other, however, the nut remains in the same fixed position on the bolt as originally set. Since the nut and bolt fastener fails to compensate for this wear, the top and bottom plates become loose since the fastener no longer provides the proper biasing force needed to maintain the plates in proper contact with the ball bearings.
This can result in a number of problems to the seat swivel device. For instance, the loosened plates may undergo a wobbling action, rather than smooth rotation. This wobbling action can be further heightened if the loosened bolt sits improperly within the bores, where excessive frictional forces between the bolt and plates can result in the wearing away of the bolt or the enlargement of the diameter of the bores. Also, the wobbling rotation caused by the loosened plates may allow the ball bearings to escape from within the bearing races.
Another disadvantage in using the prior art nut and bolt assembly occurs if the nut is not properly staked to the bolt. This usually occurs when the end portion of the bolt is not properly widened to prevent the nut from loosening on the bolt during use. If this should occur, it is possible for the nut to "retread" itself over the partially widened portion of the bolt, resulting in a lessening of the force holding the two plates together. The loosening of the nut in this manner will also cause the plates to loosen, again causing a wobbling action when the two plates undergo relative rotation. This wobbling action will increase even further as the races and ball bearings become worn during usage. Additionally, if a user leans back on a chair having a swivel with loosened plates, the plates may separate a sufficient amount to enable the ball bearings to escape from within the bearing races.
Although it is possible to retighten the nut when it loosens on these prior art devices, usually the nut and bolt are not accessible to a wrench or pliers unless the objects mounted to the plates are removed. This can be a painstaking operation to the owner since the plates must be removed and properly remounted to the object after the nut is tightened. In the case of a chair swivel, removing and replacing the mounting plates can be a clumsy and onerous job. Also, the nut might have to be restaked to the bolt in some cases, a process that requires skills and tools which are not generally possessed by most people. Further, since the wear to the races on the plates is gradual and continuous, this procedure of retightening the nut and bolt may be required at regular intervals.
Another problem associated with prior art chair swivels occurs during the manufacturing of the top and bottom mounting plates. Usually, the two plates are formed by a cold working operation in which a sheet of metal is stamped pressed in a die to create the desired shape. However, a great deal of precision is usually required during this operation to form the annular recess on each plate that defines bearing the race. Since most conventional swivel devices are formed with concave cross-sectional recesses, a great deal of precision is usually needed in matching the plates to produce upper and lower races that permit smooth rotation of the bearings. A race having minor eccentricities can cause the bearings to tighten, resulting in restricted rotation between the plates. Additionally, major eccentricities between the races could even cause the ball bearings to jam completely causing the plates to stop free rotation altogether. This problem usually occurs when the surfaces of the races do not align properly to permit each ball bearing to rotate freely. When this occurs, either or both of the mounting plates may become useless or have to be replaced with a matching plate to assure proper rotation of the bearings between the plates.
While prior art seat swivel devices are generally useful, these devices have limitations and disadvantages as illustrated above which are serious drawbacks. The present invention has as its objective the elimination of these and other disadvantages by providing a seat swivel apparatus that includes a fastener that utilizes a biasing means, such as a Belleville spring, to provide a continuous and substantially constant biasing force upon the plates to maintain them in proper rolling engagement with the ball bearings. The present invention also eliminates the two piece nut and bolt assembly by utilizing a unitary fastener known in the art as a kingpin that is cold headed over the Belleville spring to virtually eliminate the possibility that the fastener would become separated during use.
Another objective of the present invention is to provide bearing races that generally eliminate the need for extreme precision in forming and aligning the races on the mounting plates. The present invention accomplishes this by utilizing bearing races having partially flattened surfaces that allow for greater eccentricity when aligning the races on each mounting plates. Also, another aspect of the present invention is to provide bearing races that allow the ball bearings to be self-aligning and permits them to find their own center. Additionally, the races used in accordance with the present invention allow the chair swivel apparatus to be manufactured more easily and at reduced expense.